For the individual legs, there are some unique responsibilities. The starter's job is to get the race going and to make up some distance. The key to the exchange is making it later in the [20-metre pass] zone. If you really want to be fast, stretch it out to the incoming guy, who has to run after that guy—because then he's focused on running full speed all the way. And cannot slow down in the zone.
The second leg is important because if the pass is smooth, the runner is on the straight. The second and third legs can be the longest, depending on how the pass zone is run, but the second leg isn't on any curves so a good pace can actually create the illusion of making up more distance. The third-leg pass is important because if it's smooth, the team can make up the distance. As such, the second leg is really important: it's that runner's job to put the team out to the lead, and then the third leg must either extend or maintain it.
The anchor leg has two jobs: win and, hopefully, set a record. That's it.